It is common practice in the forming of flat, metal sheets to arrange a stack of such sheets at one end of a forming machine so as to enable the uppermost sheet of the stack to be lifted from the stack and introduced to the forming machine in which the sheet is subjected to one or more forming operations. When the confronting surfaces of the stacked sheets are smooth or have a film of lubricant thereon it sometimes is difficult to separate one sheet from another. It has been proposed, therefore, to provide a gap between the adjacent edges of the sheets at least at the uppermost end of the stack by means of a magnetic field, thereby facilitating the separation of the uppermost sheet from the remainder of the stack.
A stack of sheets conventionally is delivered to the loading end of a forming machine. If the magnetic separator is energized at the time the stack is delivered, the stack may become tilted as it approaches the source of the magnetic field. If the stack of sheets has to be removed from the loading end of the forming machine for any reason while the magnetic separator is energized, the stack also may be tilted as it moves away from the source of the magnetic field.
In some instances the magnets are so powerful that, as the stack of sheets approaches the magnets, some of the sheets are caused to separate from the stack and move rapidly and violently in the direction of the magnets, risking damage to the sheets, or to the apparatus on which the sheets are supported, or both.
The foregoing problems have been recognized in the past and overcome to some extent by the use of electromagnets which may be energized and de-energized at appropriate times. However, electromagnets are expensive, not always reliable, and require a power supply and control apparatus which is fairly short lived.
It also has been proposed to make use of permanent magnets to overcome the foregoing problems because the permanent magnets are less expensive and have a longer life. However, permanent magnets must be of considerable strength and must be movable away from the stack when the latter is introduced to the loading end of the forming machine so as to avoid displacement of some of the sheets as the stack approaches the permanent magnet. The movement of the permanent magnets heretofore has been accomplished by means of hydraulic or pneumatic cylinders which must be quite powerful, and therefore expensive, if the position of the stacked sheets is not to be changed as the magnets approach the stack powerful cylinders necessitate the use of often complex and expensive control systems, thereby adding to the cost of an installation.
A principal object of the present invention is to overcome the disadvantages associated with apparatus of the kind referred to above.